1. Field of the Invention
The present invention refers to a method for the generation and control of an oscillation frequency and particularly to a method for the determination of a bias current of a quartz oscillator.
2. Description of the Related Art
In the digital electronic applications it is often necessary to use an oscillator to generate an oscillating signal as synchronism reference that is stable in frequency and that has a low jitter.
Because of the necessary high precision and the requirements of frequency stability, a high frequency oscillator (for instance higher than 50 MHz) cannot use a phase locked oscillator (PLL), but rather a quartz oscillator is necessary to make the signal resonate at a harmonic frequency, for instance at the third one.
To get the required frequency stability, the oscillator bias current must be stable and compensated in temperature.
The typical value of the transconduttances (and therefore of the bias current) that are part of the transfer function calculation are determined in the design phase. It can happen that the distribution of some electric parameters (that are dependent on the building process of the integrated circuits) can cause variations in the current from one integrated circuit to another. Accordingly, not all manufactured oscillators can have the required features.